JP2005203090A - Optical pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup which can suppress the interference light caused by the neighboring layers and improve the unsteady tracking error signals detected by DPP when recording or reproducing on a multi-layer optical disk which has two or more recording layers on one side. <P>SOLUTION: This optical pickup has an optical component which suppresses the interference light caused by the neighboring layers and received by the photodetector when applied to an optical information recording medium which has at least two or more recording layers on one surface. In this way, it is possible to suppress the interference light caused by the neighboring layers and received by the photodetector, especially by the 1st and 2nd photodetectors. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical recording and / or reproducing apparatus, and more particularly, to prevent deterioration of a tracking error signal by an adjacent layer at the time of recording and / or reproducing of a multi-layer recording medium having a plurality of recording layers on one side. It is related to the optical pickup.

  Recording capacity is condensed by optical recording and / or reproducing equipment that records / reproduces arbitrary information on / from an optical disk, which is an optical information storage medium, using a condensing spot obtained by focusing laser light with an objective lens. It is determined by the size of the spot. The size S of the focused spot is determined as shown in Equation (1) by the laser light wavelength λ used and the numerical aperture (NA) of the objective lens.

したがって、光ディスクの高密度化のために光ディスクに結ばれる光スポットを小さくするためには、青色レーザーのような短波長光源及び開口数０．６以上の対物レンズ採用が必須である。

Therefore, in order to reduce the light spot connected to the optical disk in order to increase the density of the optical disk, it is essential to employ a short wavelength light source such as a blue laser and an objective lens having a numerical aperture of 0.6 or more.

  After recording a CD on which information is recorded and / or reproduced using light having a wavelength of 780 nm and an objective lens having a numerical aperture of 0.45 or 0.5, the recording density is increased and information is stored. Much research is being done to increase capacity. The result is a DVD on which information is recorded and / or reproduced using light having a wavelength of 650 nm and an objective lens having a numerical aperture of 0.6 or 0.65.

  Currently, research on high-density optical disks having a recording capacity of 20 GB or more using light having a blue wavelength, for example, a wavelength of 405 nm, is being actively conducted.

  High-density optical discs are currently being standardized actively, and some standards are almost completed, and use light of a blue wavelength, for example, 405 nm wavelength. At this time, the numerical aperture of the objective lens for the high-density optical disc is 0.65 or 0.85 as described later.

  The thickness of the CD is 1.2 mm, but the reason for reducing the thickness to 0.6 mm in the case of DVD is that the numerical aperture has increased from 0.45 in the case of CD to about 0.6 in the case of DVD. This is to ensure a tolerance due to tilting.

The coma aberration W ₃₁ generated due to the tilt of the optical disk is expressed as follows when the tilt angle of the optical disk is θ, the refractive index of the optical disk is n, the thickness of the optical disk is d, and the numerical aperture of the objective lens is NA. It can be expressed by the following relational expression.

ここで、光ディスクの屈折率及び厚さは、それぞれ光ディスクの記録及び／または再生のための光が入射される光入射面から記録層に至る光学媒質、すなわち、保護層または基板の屈折率及び厚さをいう。

Here, the refractive index and thickness of the optical disc are the optical medium from the light incident surface on which light for recording and / or reproduction of the optical disc is incident to the recording layer, that is, the refractive index and thickness of the protective layer or substrate. Say it.

  When formula (2) is taken into consideration, in order to ensure tolerance due to the tilt of the optical disk, it is necessary to reduce the thickness of the optical disk when increasing the numerical aperture of the objective lens in order to increase the density.

  There is a tendency to reduce d in order to ensure the tolerance due to the inclination of the optical disk due to higher density. The CD was reduced from 1.2 mm to 0.6 mm for DVD.

  In the case of a high-density optical disk having a capacity higher than that of a DVD, if the numerical aperture of the objective lens for the high-density optical disk is increased to, for example, 0.85, the thickness of the high-density optical disk depends on the inclination of the optical disk. In order to prevent performance degradation, it is necessary to reduce to about 0.1 mm. In this way, the Blu-ray disc (hereinafter referred to as BD) is obtained by increasing the numerical aperture of the objective lens and reducing the thickness of the optical disc. In the BD standard, the wavelength of the light source is 405 nm, the numerical aperture of the objective lens is 0.85, and the thickness of the optical disk is about 0.1 mm.

  A high-density optical disc includes AOD (Advanced Optical Disc) in addition to BD. In the AOD standard, the wavelength of the light source is 405 nm, the numerical aperture of the objective lens is 0.65, and the thickness of the optical disk is about 0.6 mm.

  Here, the thickness of the optical disk is the distance between the incident surface on which light is incident from the objective lens side and the information storage surface, and corresponds to the thickness of the substrate in the case of CDs and DVDs. In the case of BD, this corresponds to the thickness of the protective layer.

In the optical disk with the thickness reduced to 0.1 mm, the biggest problem is that the thickness must be made uniform within ± 3 μm, which is the next spherical surface caused by the optical disk thickness error Δd. It can be seen from the aberration formula _{W 40.}

ここで、ｎは光ディスクの光入射面から情報保存面に至る媒質の屈折率であり、ＮＡは開口数である。

Here, n is the refractive index of the medium from the light incident surface of the optical disk to the information storage surface, and NA is the numerical aperture.

  FIG. 1 shows the relationship between optical disk thickness error and wavefront aberration when using an objective lens with a wavelength λ = 400 nm and NA = 0.85. As can be seen in FIG. 1, when the thickness error is, for example, ± 3 μm or more, the spherical aberration generates a wavefront aberration (OPD (λ)) of 0.03λ or more.

  Therefore, in a system using a high NA such as NA = 0.85, correction and / or detection of spherical aberration is essential.

  On the other hand, in order to increase the capacity, a DVD double-layer disc in which information on the optical disc is recorded in two layers has been adopted as a standard. At this time, the distance between the two layers is about 55 μm.

  Therefore, in order to further increase the storage capacity of the high-density optical disk, it is expected that it is formed with a plurality of recording layer structures as in the case of DVD. At this time, the interlayer spacing is determined almost in proportion to the depth of focus. The

Since the depth of focus is proportional to λ / NA ² , when considering that the two-layer distance of the DVD double-layer disc is about 55 μm, the two-layer distance when the BD is composed of the two-layer disc is, for example, about 17 μm. It will be about.

  Here, a plurality of recording layer optical discs having two or more recording layers on one side can greatly increase the recording capacity as compared with a single recording layer.

  Optical discs can be classified into single-layer optical discs having a single recording layer and multi-layer optical discs having a plurality of recording layers, depending on the number of recording layers on one side. Optical discs can be classified into a single-side structure in which the recording layer is only on one side and a double-sided structure in which the recording layer is formed on both sides.

  An optical disc having two recording layers on one side is called a double-layer optical disc. This double-layer optical disc is further classified into a double-layer optical disc having a single-side structure and a double-layer optical disc having a double-side structure.

  On the other hand, a differential push-pull (DPP) method capable of correcting an offset of a push-pull signal generated during reproduction of an eccentric optical disc is generally adopted as a tracking method for a recordable optical disc. The light is separated into three orders of 0th order and ± 1st order using a diffraction grating, and at this time, the light quantity ratio of the separated light—first order: zero order: first order is 1: 10: 1 or more, that is, Increasing the amount of the zero-order light beam is advantageous in terms of light utilization efficiency.

FIG. 2 shows the structure of a photodetector 1 capable of detecting a tracking error signal by the DPP method. The light receiving areas A, B, C, and D receive zero-order light, the light-receiving areas E, F, G, and H receive ± first-order light, and the phase of ± first-order light with respect to the zero-order light. If the angle is set to 180 °, the tracking error signal TES _DPP detected by the DPP method = [(A + D) − (B + C)] − κ [(E−F) + (GH)] is obtained. The offset of the tracking error signal due to movement is corrected. Here, κ is 10 / (1 + 1) = 5 when the light quantity ratio between the zero-order beam and the ± first-order beam is 1: 10: 1.

  In the case of a two-layer optical disk, a layer near the light incident surface of the optical disk is L1, and a layer far from the light incident surface is L2. During recording and / or reproduction, light returning to the photodetector is affected not only by the layer located at the focal point of the objective lens but also by adjacent layers.

  Since the interlayer spacing determined by the standard is determined by a line that does not affect the information on the optical disc, interlayer crosstalk does not affect the servo signal in the optical pickup. .

  FIG. 3 is a schematic diagram of an optical path when reproducing a double-layer optical disc. Referring to FIG. 3, the light L12 reflected by L2 is positioned in front of the light L11 with respect to the light L11 received by the photodetector 1 during the reproduction of the L1 layer near the light incident surface. . On the other hand, the light L21 reflected by L1 is positioned behind the light L22 with respect to the light L22 received by the photodetector 1 during reproduction of the L2 layer.

  FIG. 4A shows a light distribution collected on the photodetector during reproduction of the L1 layer. FIG. 4B shows the light distribution collected on the photodetector during reproduction of the L2 layer. In FIG. 4A, the L11_0 order light, the L11_ ± 1st order light, and the L12_0 order light are respectively the 0th order light reflected by the L1 layer, the ± 1st order light reflected by the L1 layer, and the L2 layer during reproduction of the L1 layer. Represents reflected zeroth order light.

  In FIG. 4B, the L22_0 order light, the L22_ ± 1st order light, and the L21_0 order light are respectively the 0th order light reflected by the L2 layer, the ± 1st order light reflected by the L2 layer, and the L1 layer during the reproduction of the L2 layer. Represents reflected zeroth order light.

  When the 0th-order light quantity of L12 and L21 is the same as the 0th-order light quantity of L11 and L22, it corresponds to 10 times the primary light quantity of L11 and L22.

  Actually, the 0th-order light quantity of L12 and L21 is not the same as the 0th-order light quantity of L11 and L22, respectively, but it affects the primary light of L11 and the primary light of L22. Accordingly, the zero-order light of L12 and L21 is defocused but affects the tracking signal. In particular, if the L12 zero-order light and the L21 zero-order light are varied due to variations in the interlayer spacing thickness, the tracking signal fluctuates.

  FIG. 5 shows a detection signal difference signal (E−F) between the light receiving area E and the light receiving area F and a detection signal difference signal (GH) between the light receiving area G and the light receiving area H during reproduction of the L1 layer. The measurement signal of the sum signal [(E−F) + (G−H)] of the two difference signals is shown.

  As can be seen from FIG. 5, the fluctuations of the difference signal (E-F) and the difference signal (GH) are entirely in opposite phases, but even if the sum is taken, the fluctuation is compensated. Remains.

Therefore, when considering that the tracking error signal detected by the DPP method is TES _DPP = [(A + D) − (B + C)] − κ [(E−F) + (GH)], the DPP method The detected tracking error signal fluctuates due to a variation in the thickness of the interlayer spacing.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide an optical pickup capable of suppressing the interference light by the adjacent layer and improving the deterioration of the tracking error signal by the adjacent layer.

  In order to achieve the above object, the present invention provides a light source that emits light of a predetermined wavelength, an objective lens that focuses the light emitted from the light source and connects it to an optical information storage medium as a light spot, and a light path. An optical path converter for converting, a photodetector for receiving light reflected by the optical information storage medium and passing through the optical path converter to detect an information signal and / or an error signal, and a plurality of recording layers on at least one side. And an optical member for suppressing interference light from an adjacent layer from being received by the photodetector when the optical information storage medium is provided.

  Here, the optical member includes a diffraction region that diffracts part of the light reflected by the adjacent layer when an optical information storage medium having a plurality of recording layers on at least one surface is applied.

  Any one of a polarization hologram and a non-polarization hologram is formed in the diffraction region of the optical member.

  The optical member is disposed at any one position between the optical path changer and the objective lens or between the optical path changer and the photodetector.

  A quarter-wave plate for changing the polarization of incident light is further provided between the optical path changer and the objective lens.

  It further includes a liquid crystal element that generates a phase difference for correcting spherical aberration due to the thickness difference of the optical information storage medium.

  A diffraction grating is further provided that divides the light emitted from the light source into zero-order light and ± first-order light and irradiates the optical information storage medium with the zero-order light and ± first-order light.

  The photodetector includes a main photodetector that receives zero-order light reflected by the optical information storage medium, and first and first light that receives + 1st order light and −1st order light reflected by the optical information storage medium. A second sub-photodetector, wherein the optical member diffracts at least part of the zero-order light reflected by the adjacent layer so that the first and second sub-photodetectors do not receive the light. desirable.

  Here, the main photodetector has a structure divided into at least two in a direction corresponding to a radial direction and a tangential direction of the optical information storage medium, and the first and second sub photodetectors are It is desirable that the optical information storage medium has a structure that is divided into at least two in a direction corresponding to the radial direction, and can detect a tracking error signal by the DPP method.

  The photodetector further includes an auxiliary photodetector that receives zero-order light diffracted by the optical member.

  The diffractive region of the optical member is formed in a shape corresponding to the main light detector and the first and second sub light detectors of the light detector, and the zero-order light from the adjacent layer is the main light detector, the first light detector. The light is not received by the first and second sub photodetectors.

  The diffraction region of the optical member is a single region in which the zero-order light from the adjacent layer is not received by the main light detector and the first and second sub light detectors of the light detector.

  The diffraction region of the optical member is formed so that zero-order light from the adjacent layer is not received by the first and second sub photodetectors.

  The optical path converter is a polarization-dependent optical path converter.

  The light source emits blue wavelength light, and the objective lens is formed to satisfy the BD standard, and records and / or reproduces an optical information storage medium having a plurality of recording layers on at least one side of the BD standard.

  According to the present invention, it is possible to suppress the interference light from the adjacent layer from being received by the photodetector, particularly the first and second sub photodetectors of the photodetector.

  Therefore, the fluctuation of the tracking error signal is improved even when the thickness of the interlayer spacing is changed, and the tracking error signal having excellent characteristics can be detected.

  It is also possible to improve the interlayer crosstalk without causing the main photodetector of the photodetector to receive the interference light from the adjacent layer.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  6 and 7 schematically show an embodiment of the optical configuration of the optical pickup according to the present invention. The optical pickup according to the present invention includes a light source 11, an objective lens 30 that focuses light emitted from the light source 11 and connects it to a recording medium, that is, an optical disc 10, and an optical path conversion for changing the path of incident light. 6, a polarizing beam splitter shown in FIG. 6, a light detector 40 that receives light reflected by the optical disk 10 and detects an information signal and / or an error signal, and light reception by the light detector 40. An optical member 25 for diffracting a part of the light reflected by the adjacent layer at the time of recording and / or reproducing of the multilayer optical disc having a plurality of recording layers on at least one surface so that the interference light by the adjacent layer is suppressed. Consists of including.

  In addition, the optical pickup according to the present invention is a polarization-dependent optical path converter for converting the path of incident light by polarized light, for example, a polarized light, as the optical path converter so as to satisfy a high efficiency requirement in a recording optical system. A quarter wave plate 19 that includes a beam splitter 14 and changes the polarization of incident light between the polarizing beam splitter 14 and the objective lens 30 may be further included.

  The optical pickup according to the present invention preferably further includes a correction element such as a liquid crystal element 20 that generates a phase difference for correcting the spherical aberration due to the thickness difference of the optical disk 10.

  Further, the optical pickup according to the present invention converts the light emitted from the light source 11 into the 0th order light (main light) and the ± 1st order light (sublight) so as to detect the tracking error signal by the three beam method or the DPP method. A diffraction grating 12 may be further provided. A reproduction signal can be obtained from the detection signal of the 0th order light reflected by the optical disc 10, and a tracking error signal can be obtained by calculating the detection signals of the 0th order light and the ± 1st order light reflected by the optical disc 10.

  6 and 7, reference numeral 13 indicates a front light detector for monitoring the light output of the light source 11, and reference numeral 16 indicates that light emitted from the light source 11 in the form of divergent light is converted into parallel light. A collimating lens that is incident on the objective lens 30, reference numeral 15 is an astigmatism lens that generates astigmatism so that a focus error signal can be detected by the astigmatism method. Reference numeral 18 is a reflection mirror for bending the path of light, and reference numeral 23 is an actuator for driving the objective lens 30 in the focus, tracking and / or tilt directions.

The light source 11 emits light in a predetermined wavelength region, preferably light in a blue wavelength region that satisfies AOD and BD standards, for example, light having a wavelength of 405 nm.
For example, the objective lens 30 desirably has a high numerical aperture satisfying the BD standard, that is, a numerical aperture of about 0.85.

  As described above, when the light source 11 emits light in the blue wavelength region and the objective lens 30 has a numerical aperture of 0.85, the optical pickup according to the present invention has a high-density optical disc 10, particularly a BD standard optical disc 10. Can be recorded and / or reproduced.

  Here, the wavelength of the light source 11 and the numerical aperture of the objective lens 30 are variously modified. The optical configuration of the optical pickup according to the present invention can be variously modified.

  For example, so that the optical pickup according to the present invention can record and / or reproduce a DVD having a plurality of recording layers on one side, the light source emits light in a red wavelength region suitable for DVD, for example, 650 nm wavelength, and an objective lens 30 may be provided to have a numerical aperture suitable for DVD, for example, a numerical aperture of 0.65.

  Further, the optical pickup according to the present invention emits light of a plurality of wavelengths, for example, a blue wavelength suitable for a high-density optical disk and a red wavelength suitable for DVD so that BD, AOD and DVD can be used interchangeably. And the objective lens 30 may be configured to achieve an effective numerical aperture suitable for BD and DVD, or may further include a separate member for adjusting the effective numerical aperture.

  Further, the optical pickup according to the present invention has an optical configuration shown in FIG. 6 as an additional optical unit for recording and / or reproducing a high-density optical disc and recording and / or reproducing a DVD and / or CD. In some cases, a further configuration may be provided.

  On the other hand, the polarization-dependent optical path converter, for example, the polarization beam splitter 14 directs the light incident from the light source 11 side toward the objective lens 30 side, and the light reflected by the optical disc 10 toward the photodetector 40 side. Dodge. 6 and 7 show an example in which a polarization beam splitter 14 that selectively transmits or reflects incident light according to polarized light is shown as the polarization-dependent optical path converter. Alternatively, as the polarization-dependent optical path converter, for example, one polarized light emitted from the light source 11 is transmitted as it is, and another polarized light that is reflected by the optical disc 10 and incident is + 1st order or −1. Next, a polarization hologram element to be diffracted may be provided. When a polarization hologram element is provided as the polarization-dependent optical path converter, the light source 11 and the photodetector 40 can be formed into an optical module.

  When the polarizing beam splitter 14 and the quarter-wave plate 19 are provided as described above, a single linearly polarized light incident on the polarizing beam splitter 14 from the light source 11 side, for example, p-polarized light, is supplied to the polarizing beam splitter 14. Then, the light passes through the quarter-wave plate 19 and changes to a single piece of circularly polarized light through the quarter-wave plate 19, and proceeds to the optical disk 10 side. The single circularly polarized light is reflected by the optical disc 10 and becomes other circularly polarized light, and becomes another linearly polarized light, for example, s-polarized light while passing through the quarter-wave plate 19 again. The other linearly polarized light is reflected by the mirror surface of the polarization beam splitter 14 and travels toward the photodetector 40 side.

  As another example, instead of the polarization-dependent optical path changer, a beam splitter that transmits and reflects incident light at a predetermined ratio, and light emitted from the light source 11 is transmitted as it is, reflected by the optical disc 10 and incident. The light may include a hologram element that diffracts + 1st order or −1st order. When the hologram element is provided as the optical path changer, the light source 11 and the photodetector 40 can be formed into an optical module.

  Here, when considering the point that light roughly P or S-polarized light is emitted from the semiconductor laser used as the light source 11, a beam splitter, a hologram element, or the like is used instead of the polarization-dependent optical path converter. A non-polarization-dependent optical path converter can be provided, and a quarter-wave plate 19 can be disposed.

  In the correction element, the thickness from the light incident surface of the optical disc 10 to the target recording layer deviates from the design value of the objective lens 30 when recording and / or reproducing the multi-layer optical disc 10 having a plurality of recording layers on at least one surface. It is desirable to operate so as to perform a spherical aberration correction function due to a thickness difference during recording and / or reproduction of the recording layer.

  In the optical pickup according to the present invention, the correction element may include a liquid crystal element 20.

  At this time, since the liquid crystal has polarization characteristics, the liquid crystal element 20 desirably generates a phase difference selectively by polarization of incident light and power supply driving.

  That is, when the liquid crystal element 20 is in a power-on state, the thickness of the liquid crystal element 20 is changed by changing the wavefront by generating a phase difference with respect to a single polarized light traveling from the light source 11 side to the optical disk 10 side, for example, P-polarized light. When the spherical aberration due to the difference is corrected and the power is off, it is desirable to transmit the incident light as it is without generating a phase difference, that is, without changing the wavefront, regardless of the polarization of the incident light.

  At this time, the liquid crystal element 20 is different from the optical path changer so that the light incident on the liquid crystal element 20 from the light source 11 and the light reflected on the optical disk 10 and incident on the liquid crystal element 20 are different. It is desirable to arrange between the four-wave plate 19.

  In FIG. 8, S is the phase of spherical aberration generated in the light that is focused by the objective lens 30 and connected to the recording layer of the optical disk 10 due to the difference between the thickness of the optical disk 10 and the design value of the objective lens 30, that is, the wavefront. Represents. S ′ represents a phase, that is, a wavefront generated in the liquid crystal element 20 in order to correct the spherical aberration due to the thickness difference.

  The phase distributions S and S ′ in FIG. 8 indicate the light emitted from the light source 11 in the form of divergent light on the optical path between the light source 11 and the objective lens 30 as shown in FIGS. The collimating lens 16 for changing the light into parallel light is provided, and the light incident on the liquid crystal element 20 is parallel light.

  As shown in FIG. 8, since spherical aberration occurs due to the difference in thickness of the optical disk 10, the light passing through the liquid crystal element 20 becomes light having a phase distribution opposite to the phase distribution of the spherical aberration. If the liquid crystal element 20 is formed and driven so as to be incident on the optical disc 10, spherical aberration due to the thickness difference of the optical disc 10 can be corrected.

  On the other hand, as shown in FIGS. 6 and 7, when the light emitted from the light source 11 is branched into at least three light beams by the diffraction grating 12, the photodetector 40 is as shown in FIG. 9. The main light detector 240 and first and second sub-light detectors 241 and 245 for receiving the first and second sub-lights reflected by the optical disc 10 on both sides thereof may be provided.

  FIG. 9 shows an example of a photodetector 40 that can be used in the optical pickup according to the present invention and a circuit 50 for signal calculation. Referring to FIG. 9, the main light received by the main light detector 240 is zero-order diffracted light that has been transmitted straight through the diffraction grating 12, and the first and second sub-light detectors 241 and 245 receive the first and second light. The second sub-light is light diffracted by the diffraction grating 12 to the + 1st order and the −1st order.

  The main light detector 240 can detect a focus error signal and / or a tracking error signal. For example, a direction corresponding to the radial direction of the optical disc 10 (R direction) and a direction corresponding to the tangential direction (T direction). It is desirable that each is divided into two. That is, it is desirable that the main photodetector 240 has at least a four-part structure.

  FIG. 9 shows an example in which the main photodetector 240 is divided into two parts in the R direction and divided into two parts in the T direction to have a four part structure. As another example, the main photodetector 240 may have an eight-divided structure obtained by dividing into four in the R direction and dividing into two in the T direction.

  The first and second sub photodetectors 241 and 245 are preferably divided into two in the R direction so that tracking error signals can be detected by the DPP method.

  That is, the main light detector 240 is divided into at least two parts in the R direction and at least two parts in the T direction, and the first and second sub-light detectors 241 and 245 are divided into at least two parts in the R direction. It is desirable that error signal detection is possible.

  As described above, when the main photodetector 240 is divided into four or eight and the first and second sub-detectors 241 and 245 are divided into two in the R direction, tracking error signal detection by the DPP method is possible. .

  On the other hand, in order to suppress the interference light of the adjacent layer, as will be described later, when part of the light is diffracted by the optical member 25, part of the reproduction light may also be diffracted to deteriorate the reproduction signal.

  Therefore, the photodetector 40 may further include an auxiliary photodetector 247 that detects the diffracted light in a separate region and compensates the reproduction signal.

  The light receiving areas of the main light detector 240 divided into four are A, B, C, and D, the light receiving areas of the first sub-light detector 241 are E1, E2, and the light receiving areas of the second sub-light detector 245, respectively. F1 and F2, and the light receiving area of the auxiliary light detector 247 is M, the divided structure of the photodetector 40 as shown in FIG. 9 and the present invention as shown in FIGS. The focus error signal FES, tracking error signal TES, and information reproduction signal RF-SUM obtained by the optical configuration of the optical pickup are as shown in Table 1, for example. Here, for the sake of convenience, each light receiving region and a signal detected thereby are represented by the same reference numeral.

表１で、κはゲインであり、ＲＯＭは再生専用光ディスク、記録可能型はＲ、ＲＷ、ＲＡＭ型のような記録可能な光ディスクまたはＢＤ、ＡＯＤのような記録可能な高密度光ディスクを表す。ここで、ＤＰＰは主にＲＡＭ型光ディスクやＢＤで主に使われ、プッシュプルなどはＲ／ＲＷ型光ディスクで主に使われる。もちろん、ＤＰＰはＲＡＭ及びＢＤだけでなく、Ｒ／ＲＷでも使用可能である。

In Table 1, κ is a gain, ROM is a read-only optical disk, recordable type is a recordable optical disk such as R, RW, RAM type or recordable high-density optical disk such as BD or AOD. Here, DPP is mainly used for RAM type optical disks and BDs, and push-pull is mainly used for R / RW type optical disks. Of course, DPP can be used not only for RAM and BD but also for R / RW.

  FIG. 9 shows an example in which the circuit 50 is provided to detect a tracking error signal TES according to the DPP method, that is, the DPP signal and the information reproduction signal RF_SUM.

  On the other hand, as described above with reference to FIGS. 3, 4A and 4B, when recording and / or reproducing an optical disk having a plurality of recording layers on at least one surface, the light returning to the photodetector is transmitted from the objective lens. This includes not only the recording and / or reproducing target layer located at the focal point, but also the interference light from the adjacent layer.

  At this time, the light from the adjacent layer that overlaps with the 0th order and ± 1st order light reflected by the recording and / or reproduction target layer is the 0th order light.

  Therefore, the optical member 25 can include a diffraction region, for example, a hologram region, that diffracts part of the light reflected by the adjacent layer when recording and / or reproducing a multilayer optical disc having a plurality of recording layers on at least one surface.

  The first and second sub-detectors 241 and 245 receive light by diffracting zero-order light from the adjacent layer that overlaps at least ± first-order light reflected by the target layer by the hologram region of the optical member 25. As a result, interference light from the adjacent layer can be suppressed.

  The optical member 25 includes a hologram region having the same or similar structure as that of the photodetector 40 shown in FIG. 9, and diffracts the interference light using the hologram region in order to suppress the interference light by the adjacent layer. Let

  10A to 10C show various examples of the hologram region of the optical member 25. FIG. In addition, the hologram area on the optical member 25 can be variously modified.

  FIG. 10A shows a hologram region in which the optical member 25 diffracts the zero-order light by the adjacent layer in a form corresponding to the main photodetector 240 and the first and second sub-detectors 241 and 245 of the photodetector 40. An example provided with H.251 is shown.

  FIG. 10B shows a single hologram in which the optical member 25 prevents the main light detector 240 and the first and second sub-light detectors 241 and 245 of the light detector 40 from receiving zero-order light from the adjacent layer. An example provided with a region 253 is shown.

  FIG. 10C shows an example in which the optical member 25 includes a hologram region 255 that diffracts the 0th-order light from the adjacent layer in a form corresponding to the first and second sub-detectors 241 and 245 of the photodetector 40.

  In the case of FIG. 10A and FIG. 10B, neither the main light detector 240 nor the first and second sub-light detectors 241 and 245 receive zero-order light from the adjacent layer.

  In the case of FIG. 10C, the first and second sub-detectors 241 and 245 do not receive zero-order light from the adjacent layer, but the main photodetector 240 receives zero-order light from the adjacent layer. Indicates.

  The difference between the zero-order light reflected by the target layer and the zero-order light reflected by the adjacent layer is large, so that the difference signal used to detect the tracking error signal by the DPP method, that is, (B + C) The 0th order light from the adjacent layer does not significantly affect the − (A + D) signal.

  However, since the light amount difference between the ± first order light reflected by the target layer and the zero order light reflected by the adjacent layer is not relatively large, as described above with reference to FIG. The signal used to detect the signal, that is, the (EF) + (GH) signal is significantly affected by the 0th order light from the adjacent layer.

  Therefore, in order to suppress the fluctuation of the tracking signal, the 0th order light from the adjacent layer is overlapped with the ± 1st order light reflected by the target layer and received by the first and second sub photodetectors 241 and 245. It is important to prevent this from happening.

  The optical member 25 having various hologram regions 251, 253, and 255 shown in FIGS. 10A to 10C satisfies such a requirement.

  Assume that the optical pickup according to the present invention is applied to the double-layer optical disc shown in FIG. As described above with reference to FIG. 3, the light L12 reflected by L2 is ahead of the light L11 with respect to the light L11 received by the photodetector when reproducing the L1 layer near the light incident surface. On the other hand, the light L21 reflected by L1 is positioned behind the light L22 with respect to the light L22 received by the photodetector during reproduction of the L2 layer.

  In this case, the light distribution reflected by the double-layer optical disc and condensed on the photodetector 40 via the optical member 25 is as shown in FIGS. 11A and 11B.

  FIG. 11A shows the light distribution collected on the photodetector during reproduction of the L1 layer. FIG. 11B shows the light distribution collected on the photodetector during reproduction of the L2 layer. 11A and 11B show an example in which the optical member 25 includes the hologram region 251 shown in FIG. 10A.

  In FIG. 11A, the L11_0 order light, the L11_ ± first order light, and the L12_0 order light are respectively the 0th order light reflected by the L1 layer and the ± 1st order reflected by the L1 layer during reproduction of the L1 layer, as in FIG. 4A. Light, 0th order light reflected by the L2 layer. In FIG. 11A, L1M represents the light diffracted by the hologram region 251 of the optical member 25.

  In FIG. 11B, the L22_0 order light, the L22_ ± first order light, and the L21_0 order light are respectively the 0th order light reflected by the L2 layer and the ± 1st order reflected by the L2 layer during the reproduction of the L2 layer, respectively. Light, 0th order light reflected by the L1 layer. In FIG. 11B, L2M represents light diffracted by the hologram region 251 of the optical member 25.

  11A and 11B, when the optical pickup according to the present invention is applied, the first and second sub-detectors 241 and 245 are overlapped with the ± first-order light reflected by the target layer. Thus, it is possible to prevent the 0th order light reflected by the adjacent layer from being received.

  Therefore, since interference light by the adjacent layer in the light receiving region of the ± primary light for the DPP signal is effectively suppressed, fluctuation of the tracking error signal due to the interference light by the adjacent layer can be greatly improved.

  FIG. 12 shows a difference signal (E−F) between the detection signals of the light receiving region E and the light receiving region F and the detection signals of the light receiving region G and the light receiving region H when the L1 layer of the optical disc 10 is reproduced by the optical pickup according to the present invention. A difference signal (G−H), and a measurement signal of the sum signal [(E−F) + (G−H)] of the two difference signals.

  As can be seen from FIG. 12, the difference signal (EF) and the difference signal (GH) hardly fluctuate, and the two difference signals (E-F) and the difference signal (GH) are mutually different. Since it has the opposite phase, the shaking is further improved when taking the sum. If FIG. 5 and FIG. 12 are compared with each other, it can be seen that the fluctuation of the signal is remarkably improved.

As described above, when the optical pickup according to the present invention is applied, the tracking error signal detected by the DPP method is TES _DPP = [(A + D) − (B + C)] − κ [(E−F) + (GH). ], The tracking error signal detected by the DPP method hardly fluctuates due to the thickness variation of the interlayer spacing.

  On the other hand, in FIGS. 6 and 7, an example in which the optical member 25 is disposed between the light source 11 and the quarter-wave plate 19, more preferably between the optical path converter and the quarter-wave plate 19. Show. As shown in FIGS. 6 and 7, the optical pickup according to the present invention includes the quarter-wave plate 19, and the optical member 25 is disposed between the optical path converter and the quarter-wave plate 19. In other words, the hologram region 251, 253 or 255 of the optical member 25 is formed with a polarization hologram that selectively diffracts according to the polarization of the incident light so as to diffract only the light that is reflected by the optical disc 10. desirable.

  For example, when the light emitted from the light source 11 and traveling toward the objective lens 30 is P-polarized light, the polarization hologram transmits the P-polarized light traveling toward the objective lens 30 straight as it is and is reflected by the optical disk 10 as 1 It is desirable that only light changed to S-polarized light is diffracted through the / 4 wavelength plate 19.

  As described above, the reason why the polarization hologram is formed on the optical member 25 so that the light traveling from the light source 11 side to the objective lens 30 side is not diffracted is that part of the light directed toward the optical disk 10 side is the optical member 25. This is because the intensity of the converging spot is lost due to the diffraction of the light and the intensity of the focused spot is weakened, thereby preventing a decrease in the amount of recording light and / or deterioration of the reproduction signal.

  On the other hand, in order to improve the fluctuation of the tracking error signal, the optical member 25 is diffracted so that the 0th-order light reflected by the adjacent layer is diffracted so that it is not received by the first and second sub-detectors 241 and 245. When the hologram regions 251 and 253 shown in FIG. 10A and FIG. 10B are provided, part of the 0th order light reflected by the target layer is also diffracted together with the 0th order light reflected by the adjacent layer. Therefore, since the 0th-order light reflected by the adjacent layer is not received by the main photodetector 240, there is an effect that interference light affecting the reproduction signal can be blocked and interlayer crosstalk of the reproduction signal can be improved.

  Of course, when the optical member 25 includes the hologram regions 251 and 253 shown in FIGS. 10A and 10B, a part of the zero-order light reflected by the target layer is also combined with the zero-order light reflected by the adjacent layer. Diffracted.

  In consideration of this, in order to prevent the reproduction signal from being deteriorated during information reproduction, the auxiliary light detector 247 detects the 0th-order diffracted light (for example, L1M and L2M lights in FIGS. 11A and 11B). The information reproduction signal RF_SUM may be detected by adding the detection signal of the auxiliary light detector 247 and the detection signal of the main light detector 240 together.

  When the optical member 25 includes the hologram region 255 shown in FIG. 10C, the 0th-order light reflected by the target layer is not diffracted, so that auxiliary light added for the purpose of preventing deterioration of the reproduction signal The detector 247 can be removed.

  Even if the reproduced signal is slightly deteriorated, the auxiliary photodetector 247 can be removed even if the crosstalk between layers is to be improved.

  As described above, when the photodetector 40 does not have the auxiliary photodetector 247, the adder immediately before the RF signal output terminal is removed by the circuit 50 shown in FIG.

  On the other hand, in the above description, the optical member 25 is disposed between the optical path changer and the quarter wavelength plate 19 and a polarization hologram is formed on the optical member 25 as an example. It is not limited.

  That is, the optical pickup according to the present invention may not include the quarter-wave plate 19, but in this case as well, the optical member 25 is disposed between the optical path changer and the objective lens 30, and the optical member 25 A polarization hologram can be formed. At this time, the reason why the polarization hologram can be formed on the optical member 25 is that the semiconductor laser used as the light source 11 emits substantially S or P-polarized light, so that the polarization hologram is converted into linearly polarized light emitted from the light source 11. May be formed so as to be diffracted. In this case, the zero-order light from the adjacent layer that is reflected by the optical disc 10 is diffracted and is not received by at least the first and second sub-detectors 241 and 245 of the photodetector 40. Of course, the light traveling from the light source 11 side to the objective lens 30 side is also diffracted by the optical member 25, but this diffracted light is not used as effective light. Therefore, if the light loss is accepted, the optical member 25 in which the polarization hologram is formed between the optical path converter and the objective lens 30 without using the quarter wavelength plate 19 can be used.

  Further, the optical pickup according to the present invention can arrange the optical member 25 on which the non-polarized hologram is formed between the optical path changer and the objective lens 30 with or without the quarter wavelength plate 19. . Also in this case, not only the light that travels after being reflected by the optical disk 11, but also the light that travels from the light source 11 side to the objective lens 30 side is diffracted by the optical member 25 on which the non-polarization hologram is formed. Such a structure can be used.

  On the other hand, the optical member 25 may be disposed between the optical path changer, that is, between the polarization beam splitter 14 and the photodetector 40.

  As described above, when the optical member 25 is disposed between the polarization beam splitter 14 and the photodetector 40, the light passes through the optical member 25 only once, so that the hologram region formed in the optical member 25 251, 253 or 255 may be a non-polarization hologram or a polarization hologram.

  The embodiment in which the optical member 25 is disposed between the polarization beam splitter 14 and the photodetector 40 can be sufficiently inferred from the above description, and thus illustration thereof is omitted.

  As described above, the type of hologram formed on the optical member 25 and the arrangement position of the optical member 25 can be variously modified. What is important is that at least the main light detector 240 and / or the first and second sub-light detectors 241 and 245 of the light detector 40 receive the zero-order light reflected by the optical member 25 on the adjacent layer of the optical disk 10. In other words, the interference light by the adjacent layer can be suppressed.

  FIG. 13 is a diagram schematically showing the configuration of an optical recording and / or reproducing device employing the optical pickup according to the present invention. Referring to FIG. 13, the optical recording and / or reproducing device is installed on a spindle motor 455 for rotating an optical disk 10 that is an optical information storage medium, and is movably installed in the radial direction of the optical disk D to / from the optical disk. An optical pickup 450 for recording and / or reproducing information, a drive unit 457 for driving the spindle motor 455 and the optical pickup 450, and a control unit 459 for controlling the focus and tracking servo of the optical pickup 450, and the like. Including. Here, reference numeral 452 represents a turntable, and 453 represents a clamp for chucking the optical disk 10.

  The optical pickup 450 has the optical pickup optical system structure according to the present invention as described above.

  The light reflected from the optical disk 10 is detected through a photodetector provided in the optical pickup 450 and is photoelectrically converted into an electrical signal. This electrical signal is input to the control unit 459 through the drive unit 457. . The drive unit 457 controls the rotational speed of the spindle motor 455, amplifies the input signal, and drives the optical pickup 450. The control unit 459 again sends a focus servo, tracking servo, and / or tilt servo command adjusted based on the signal input from the drive unit 457 to the drive unit 457, and performs the focusing, tracking, and / or tilt operations of the optical pickup 450. To embody.

  In such an optical recording and / or reproducing apparatus employing the optical pickup according to the present invention, it is possible to suppress interference light from adjacent layers during recording and / or reproduction of a multi-layer optical disk having a plurality of recording layers on one side, and to perform DPP. The fluctuation of the tracking error signal detected by can be improved.

  The present invention can be applied to optical recording and / or reproducing equipment.

It is a figure which shows the relationship between the thickness error of an optical disk, and a wavefront aberration at the time of use of the objective lens of wavelength (lambda) = 400nm and NA = 0.85. It is a figure which shows the structure of the photodetector which can detect the tracking error signal by a DPP system. It is a schematic diagram of the optical path at the time of reproduction | regeneration of a double layer optical disk. It is a figure which shows the light distribution condensed on the photodetector at the time of L1 layer reproduction | regeneration. It is a figure which shows the light distribution condensed on the photodetector at the time of L2 layer reproduction | regeneration. During reproduction of the L1 layer in FIG. 4A, a detection signal difference signal (EF) between the light receiving region E and the light receiving region F, and a detection signal difference signal (GH) between the light receiving region G and the light receiving region H, It is a figure which shows the measurement signal of the sum signal [(EF) + (GH)] of the said two difference signals. 1 is a perspective view schematically showing an embodiment of an optical configuration of an optical pickup according to the present invention. FIG. 7 is an arrangement plan view of the optical pickup in FIG. 6. It is a figure which shows the principle by which spherical aberration is correct | amended by the correction element of the optical pick-up of FIG. FIG. 7 is a diagram illustrating the structure of the photodetector in FIG. 6 and a circuit for detecting a tracking error signal (DPP signal) and an information reproduction signal (RF signal) according to the DPP method according to FIG. It is a figure which shows the various Example of the hologram area of the optical member of FIG. It is a figure which shows the various Example of the hologram area of the optical member of FIG. It is a figure which shows the various Example of the hologram area of the optical member of FIG. It is a figure which shows the light distribution condensed on a photodetector at the time of L1 layer reproduction | regeneration of an optical disk using the optical pick-up of FIG. It is a figure which shows the light distribution condensed on a photodetector at the time of L2 layer reproduction | regeneration of an optical disk using the optical pick-up of FIG. When reproducing the L1 layer of the optical disc by the optical pickup according to the present invention, the difference signal (E−F) between the detection signals of the light receiving area E and the light receiving area F and the difference signal (G -H) is a diagram showing a measurement signal of a sum signal [(EF) + (GH)] of the two difference signals. It is a figure which shows schematically the structure of the optical recording and / or reproducing | regenerating apparatus which employ | adopted the optical pick-up by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical disk 11 Light source 12 Diffraction grating 13 Front photo detector 14 Polarization beam splitter 15 Astigmatism lens 16 Collimate lens 18 Reflection mirror 19 1/4 wavelength plate 20 Liquid crystal element 25 Optical member 30 Objective lens 40 Photo detector

Claims (51)

A light source that emits light of a predetermined wavelength, an objective lens that focuses the light emitted from the light source and connects the light information storage medium as a light spot, an optical path converter that converts a light path, and an optical information storage medium A light detector that receives the light reflected by the light path converter and detects an information signal and / or an error signal;
An optical pickup comprising: an optical member that suppresses interference light from an adjacent layer from being received by the photodetector when an optical information storage medium having a plurality of recording layers on at least one surface is applied.   2. The optical member according to claim 1, further comprising a diffraction region that diffracts a part of the light reflected by the adjacent layer when an optical information storage medium having a plurality of recording layers on at least one surface is applied. Optical pickup.   The optical pickup according to claim 2, wherein one of a polarization hologram and a non-polarization hologram is formed in the diffraction region of the optical member.   The light according to claim 3, wherein the optical member is disposed at any one position between the optical path changer and the objective lens or between the optical path changer and the photodetector. pick up.   5. The optical pickup according to claim 4, further comprising a quarter-wave plate for changing the polarization of incident light between the optical path changer and the objective lens.   6. The optical pickup according to claim 5, further comprising a liquid crystal element that generates a phase difference for correcting spherical aberration due to a difference in thickness of the optical information storage medium.   The light according to claim 2, wherein the optical member is disposed at any one position between the optical path changer and the objective lens or between the optical path changer and the photodetector. pick up.   A diffraction grating is further provided that divides the light emitted from the light source into zero-order light and ± first-order light and irradiates the optical information storage medium with the zero-order light and ± first-order light. Item 8. The optical pickup according to any one of Items 1 to 7. The photodetector is
A main photodetector for receiving zero-order light reflected by the optical information storage medium;
First and second sub-light detectors for receiving + 1st order light and -1st order light reflected by the optical information storage medium,
9. The light according to claim 8, wherein the optical member diffracts at least part of the zero-order light reflected by the adjacent layer so as not to be received by the first and second sub-photodetectors. pick up. The main photodetector has a structure that is divided into at least two parts in a direction corresponding to a radial direction and a tangential direction of the optical information storage medium,
The first and second sub photodetectors have a structure that is divided into at least two in a direction corresponding to a radial direction of the optical information storage medium, and can detect a tracking error signal by a DPP method. The optical pickup according to claim 9.   The optical pickup according to claim 9, wherein the photodetector further includes an auxiliary photodetector that receives zero-order light diffracted by the optical member.   The diffractive region of the optical member is formed in a shape corresponding to the main light detector and the first and second sub light detectors of the light detector, and the zero-order light from the adjacent layer is the main light detector, the first light detector. The optical pickup according to claim 9, wherein the optical pickup is not received by the first and second sub photodetectors.   The diffractive region of the optical member includes a single region in which zero-order light from the adjacent layer is not received by the main light detector and the first and second sub light detectors of the light detector. The optical pickup described in 1.   The optical pickup according to claim 9, wherein the diffraction region of the optical member is formed so that zero-order light from an adjacent layer is not received by the first and second sub photodetectors.   8. The optical pickup according to claim 1, further comprising a quarter-wave plate that changes polarization of incident light between the optical path changer and the objective lens. 9.   The optical pickup according to claim 15, further comprising a liquid crystal element that generates a phase difference for correcting spherical aberration due to a difference in thickness of the optical information storage medium.   The optical pickup according to claim 15, wherein the optical path converter is a polarization-dependent optical path converter.   The light source emits light of a blue wavelength, and the objective lens is formed to satisfy the BD standard, and records and / or reproduces an optical information storage medium having a plurality of recording layers on at least one surface of the BD standard. The optical pickup according to claim 1, wherein: A light source that emits light;
An objective lens for focusing the emitted light on a recording / reproducing medium having a layer adjacent to the recording / reproducing layer;
A photodetector that receives light reflected from the recording / reproducing medium and detects an information signal and / or an error signal;
When the light detector receives light reflected from the recording / reproducing medium, recording and / or reproduction of the recording / reproducing layer is performed to prevent interference induced by light reflected from the adjacent layer. An optical pickup comprising: an optical member that diffracts part of the light reflected from the adjacent layer.   The optical pickup according to claim 19, further comprising an optical path converter that converts a path of incident light by its polarization so as to satisfy a high efficiency requirement of the recording optical system.   The optical pickup according to claim 20, wherein the optical path converter includes a polarization beam splitter.   The optical pickup according to claim 21, further comprising a quarter-wave plate for changing the polarization of incident light between the polarizing beam splitter and the objective lens.   20. The optical pickup according to claim 19, further comprising a correction element that generates a phase difference for correcting spherical aberration due to a thickness difference of the recording / reproducing medium.   The optical pickup according to claim 23, wherein the correction element includes a liquid crystal.   The optical pickup according to claim 19, further comprising a grating that diffracts the light emitted from the light source into zero-order light and ± first-order light so that a tracking error signal is detected.   26. The optical pickup according to claim 25, wherein the reproduction signal is obtained from the detection signal of the 0th order light, and the tracking error signal is obtained from calculation of the detection signals of the 0th order light and the ± 1st order light.   20. The optical pickup according to claim 19, wherein the light source emits light having a wavelength of about 405 nm, and the objective lens has a numerical aperture of about 0.85.   28. The optical pickup according to claim 27, wherein a high-density optical disc satisfying BD is recorded and / or reproduced.   20. The optical pickup according to claim 19, wherein the light source emits light having a wavelength of about 650 nm, and the objective lens has a numerical aperture of about 0.65.   30. The optical pickup according to claim 29, wherein a DVD having a plurality of recording layers on one side is recorded and / or reproduced.   The light source includes an optical module that emits light having a plurality of wavelengths separated from each other so that BD, AOD, and DVD can be used interchangeably, and the objective lens has an effective numerical aperture that is suitable for both BD and DVD. The optical pickup according to claim 19, further comprising a separate member for adjusting the effective numerical aperture.   25. The optical pickup according to claim 24, wherein the liquid crystal has polarization characteristics and generates a phase difference by the polarization of incident light and the operation of a power source.   When the power is turned on, the liquid crystal generates a phase difference in the polarized light from the light source toward the recording / reproducing medium and transforms its wavefront, thereby causing the spherical aberration induced by the thickness difference. The light according to claim 32, wherein when correcting and turning off the power, the liquid crystal does not generate any phase difference regardless of the polarization of the incident light, and transmits all incident light as it is. pick up.   33. The optical pickup according to claim 32, wherein the liquid crystal is capable of correcting spherical aberration by reversing the phase distribution of transmitted light to the phase distribution of spherical aberration. When light emitted from the light source is branched into at least three lights by the grating,
The photodetector is
A main photodetector;
And first and second sub-light detectors that are positioned on both sides of the main photodetector and receive light diffracted by the grating and reflected from the recording / reproducing medium. The optical pickup according to claim 25.   The main light received by the main photodetector is zero-order diffracted light that travels straight through the grating, and the first and second sub-lights received by the first and second sub-detectors are the grating. 36. The optical pickup according to claim 35, wherein the light is diffracted by + 1st order and -1st order.   The main photodetector is divided into two in the radial direction and the tangential direction of the recording / reproducing medium, or four in the radial direction of the recording / reproducing medium so that a focus error signal and / or a tracking error signal can be detected. 37. The optical pickup according to claim 36, wherein the optical pickup has an eight-divided structure that is divided into two parts in the tangential direction.   38. The optical pickup of claim 37, wherein the first and second sub photodetectors are divided into two in the radial direction so that a tracking error signal is detected using a DPP method.   The main photodetector is divided into at least two parts in the radial direction and at least two parts in the tangential direction so that the tracking error signal is detected by the DPP method, and the first and second sub photodetectors are arranged in the radial direction. The optical pickup according to claim 38, wherein the optical pickup is divided into at least two in the direction.   The main photodetector is divided into four or eight so that the tracking error signal can be detected by the DPP method, and the first and second sub-detectors are divided into two in the radial direction. 40. The optical pickup according to claim 39. In order to suppress interference light by the adjacent layer, part of the light is diffracted by the optical member, and part of the reproduction light is also diffracted to induce reproduction signal degradation,
41. The optical pickup according to claim 40, wherein the photodetector includes an auxiliary photodetector that detects diffracted light in the separated region and corrects a reproduction signal.   42. The optical pickup according to claim 41, wherein the optical member includes a diffraction region for diffracting a part of light reflected from an adjacent layer during recording and / or reproduction of the recording / reproducing medium.   43. The optical pickup according to claim 42, wherein the diffraction area is a hologram area that suppresses interference light from an adjacent layer among lights incident on the first and second sub-light detectors.   44. The optical pickup according to claim 43, wherein the optical member includes a hologram region corresponding to a form of the main photodetector first and second sub photodetectors.   The optical member includes a single hologram region for preventing zero-order light from an adjacent layer from being received by the main photodetector and the first and second sub photodetectors. 43. The optical pickup according to 43.   44. The optical pickup according to claim 43, wherein the optical member includes a hologram region corresponding to the form of the first and second sub photodetectors.   The 0th order light reflected from the adjacent layer is not overlapped with the ± 1st order light reflected from the recording / reproducing layer, and the 0th order light reflected from the adjacent layer by the first and second sub photodetectors. The optical pickup according to claim 46, wherein the optical pickup is not received.   45. The optical pickup according to claim 44, further comprising a polarization hologram in the hologram area.   The optical pickup according to claim 46, further comprising a polarization hologram in the hologram region.   Part of the 0th order light reflected from the recording / reproducing layer is diffracted together with the 0th order light reflected from the adjacent layer, and interference light affecting the reproduced signal is crossed between the two layers of the reproduced signal. 49. The optical pickup according to claim 48, wherein the optical pickup is blocked to reduce talk. A light source that emits light;
An objective lens for focusing the emitted light on a recording / reproducing medium having a recording / reproducing layer and an adjacent layer;
A main light detector that receives light reflected from the recording / reproducing medium and detects an information signal and / or an error signal; and first and second sub-light detectors;
The main light so as to diffract part of the light reflected from the adjacent layer during recording and / or reproduction of the recording / reproducing layer to prevent interference due to zero-order light reflected from the adjacent layer. An optical pickup comprising an optical member having a diffraction region corresponding to the form of the detector and the first and second sub photodetectors.

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